ආලෝකයේ වේගය ඉක්මවා යමු.
Light Pulse Faster than Light
A recent experiment* at NEC Research Institute, Princeton, N.J., U.S.A., clearly demonstrated superluminal propagation of a light pulse through a specially engineered medium. Superluminal implies faster than the speed of light, and in this experiment the peak of the light pulse arrives at the output end of the medium even before it has entered the medium.
Confusing ? Yes. Sounds exotic ? Yes. Impossible? Not anymore.These first reactions, I hope, transform into Wow ! Incredible ! Neat ! ......
The experiment has created a great deal of excitement and rekindled discussions on a variety of fundamental issues like, the validity of Einstein's Special Theory of Relativity, the Principle of Causality, the possibility of a signal travelling faster than the speed of light in vacuum and so on. None of the principles or theories are violated, however, The question as to whether this light pulse can be considered a signal is much debated and complicated one. The smooth light pulse used in the experiment has a finite spectrum (limited number of colors or frequencies); however, traditionally a true signal is one with an infinite spectrum. We will not get into this discussion but focus mainly on the experiment itself and the basic physics involved.
In a nutshell, the observed superluminal velocity of a light pulse arises due to temporally advanced rephasing of different frequency components which have undergone anomalous dispersion inside an active medium.
Let us take this step by step: we will first discuss dispersion - compare normal versus anomalous dispersion, then look at what comprises a light pulse, its group velocity in contrast to the phase velocity, and lastly use these ideas to better appreciate the experiment.
To Read More Refer This
http://www.iitk.ac.in/infocell/Archive/dirjuly3/science_light.html
Light Pulse Faster than Light
A recent experiment* at NEC Research Institute, Princeton, N.J., U.S.A., clearly demonstrated superluminal propagation of a light pulse through a specially engineered medium. Superluminal implies faster than the speed of light, and in this experiment the peak of the light pulse arrives at the output end of the medium even before it has entered the medium.
Confusing ? Yes. Sounds exotic ? Yes. Impossible? Not anymore.These first reactions, I hope, transform into Wow ! Incredible ! Neat ! ......
The experiment has created a great deal of excitement and rekindled discussions on a variety of fundamental issues like, the validity of Einstein's Special Theory of Relativity, the Principle of Causality, the possibility of a signal travelling faster than the speed of light in vacuum and so on. None of the principles or theories are violated, however, The question as to whether this light pulse can be considered a signal is much debated and complicated one. The smooth light pulse used in the experiment has a finite spectrum (limited number of colors or frequencies); however, traditionally a true signal is one with an infinite spectrum. We will not get into this discussion but focus mainly on the experiment itself and the basic physics involved.
In a nutshell, the observed superluminal velocity of a light pulse arises due to temporally advanced rephasing of different frequency components which have undergone anomalous dispersion inside an active medium.
Let us take this step by step: we will first discuss dispersion - compare normal versus anomalous dispersion, then look at what comprises a light pulse, its group velocity in contrast to the phase velocity, and lastly use these ideas to better appreciate the experiment.
To Read More Refer This
http://www.iitk.ac.in/infocell/Archive/dirjuly3/science_light.html
